OBJECTIVES: 1) Biological and biochemical characterization of the role of tissue-specific cognins (cell-cell ligands) in the mechanism of embryonic cell recognition, cell associations and cell interactions into tissues. 2) Cellular localization of glutamine synthetase induced by adrenal corticosteroids in the neural retina of chick embryos and the significance of this induction (and of the enzyme-containing cells) in the development and differentiation of the retina. 3) Modification by BrdU of the competence of embryonic neural retina cells for induction of glutamine synthetase and for normal morphogenesis. 4) Isolation from embryonic neural retina cells of mRNA for glutamine synthetase; its use in molecular hybridization studies to elucidate the mechanisms of glutamine synthetase induction in the retina.